In a conventional waveguide connection structure, the structure for connecting together a waveguide (i.e., a through hole) through which electromagnetic waves are transmitted and that is provided in an organic dielectric substrate (i.e., a connection member) and another waveguide that is provided in a metal waveguide substrate is configured such that a conductor in the through hole is electrically connected to the metal waveguide substrate so that electric potentials are maintained at the same level, for the purpose of preventing the electromagnetic waves from being reflected, having a passage loss, and leaking at the connection part (see, for example, Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-open No. 2001-267814 (paragraph [0028] and FIG. 1)